This invention pertains to a method of transportation and more particularly to a method of transporting a deck section for an offshore platform from the fabrication area to a seagoing barge.
At its Greens Bayou yard the Western Hemisphere Marine Cosntruction division of Brown & Root, Inc., has for a number of years constructed both deck sections and jacket templates for offshore platforms. An early form of platform construction is shown in U.S. Pat. No. 2,653,451 to S. E. McCullough assigned to Brown and Root, Inc.
A jacket template, or more simply a jacket as it is usually called, comprises a plurality of pipes with slight batter assembled together with cross bracing. A jacket is lowered to rest on the sea floor. Piling is driven through the pipes into the floor. Sometimes the pipes are then filled with cement grout. There is thus constructed an offshore tower. One or more such towers are used to support the legs of an above water deck composed of one or more sections. Usually there is one deck section per tower although sometimes there may be more than one section per tower, for thesize of the deck section is limited by the elevating capacity of the marine derrick barge, while the jackets need not be lifted completely off the barge to be launched and hence are not limited in size by derrick barge capacity.
A deck section typically comprises an elongated deck, e.g. rectangular, with legs extending down below the deck, the legs being disposed in two rows extending longitudinally of the deck, one row adjacent each side of the deck, there being several (more than two) legs in each row. It is to the transporation of this type of deck section to which the present invention is particularly directed although in its broader aspects the invention is also applicable to deck sections of any shape, e.g. deck sections with square decks supported on four legs.
Jackets have been fabricated lying on their sides. A jacket is moved from the fabricating yard to a barge by sliding it lengthwise over skids onto the end of an elongated barge which is disposed with one end grounded to the dock head.
Deck sections have been fabricated in erect position with their lengths parallel to the dock head and slid laterally on skids onto an elongated barge lying with its length parallel to the deck section. Such lateral loading has usually been thought to be desirable in order to avoid undue stress on the deck section when it was disposed half on the barge and half on the dock. With one row of legs on the barge and one on the dock, load is evenly distributed even if the barge rises or falls relative to the dock head. If endwise loading is attempted, uneven loading can occur with, for example, one leg of each row on the barge and three legs on the dock, should the barge rise or fall. It is believed that in the past endwise loading of a deck section onto a barge required calm water and change of ballasting of the barge during loading to avoid the danger of destructive loads being imposed on the deck section. However, lateral loading of the deck section on the barge is also difficult and dangerous due to the need for ballasting the barge to maintain lateral stability during loading. A small error in ballasting can cause the barge to roll over sideways. The time consumed for such an operation has been several hours.
To give a better idea of the problem involved, it may be noted that a typical deck section may be 180 feet long by 85 feet wide and weight over a thousand tons. The top deck may be close to 60 feet above ground with the unbraced legs extending forty feet down from the lower deck. Each leg is a pipe several feet in diameter with a conical stabing point at its lower end to be set in a socket on top of an offshore tower.
In about 1973 Brown and Root, Inc. commenced a yard improvement program. The present invention arose as part of that program.